Tubes are the building blocks of most human organs. Defects in tube development cause serious birth defects, while defects in tube maintenance underlie many common health problems such as kidney disease, heart disease and stroke. It is therefore important to understand how tubes initially form and are maintained. Unicellular tubes are a special class of very tiny tubes, just one cell in diameter. Mammals have many such tubes in the capillary beds that interface with organs such as the brain and kidney. Unicellular tubes also appear to be precursors to larger bore tubes in the vasculature. Despite this, very little is known about how unicellular tubes develop in vivo or to what degree they rely on the same polarity pathways as more complex multicellular tubes. We will identify molecular requirements for unicellular tube development and maintenance in the C. elegans excretory system, a simple renal-like organ consisting of only 3 unicellular tube cells. We've identified the EGF-Ras-ERK pathway and multiple other genes as important for tube development or maintenance in this organ. We will use these and other existing mutants to gain insight into two main questions. Aim 1) What establishes apical inward polarity and controls where epithelial junctions form to create a unicellular tube? We will (a) use live imaging to visualize tubulogenesis in WT and various mutants to ask what patterns of cell contact favor unicellular tube development~ (b) Systematically test the requirements for known polarity regulators in unicellular tube development~ and (c) Conduct unbiased genetic screens to find more genes important for unicellular tube development. Aim 2) Once formed, how are unicellular tube junctions and lumen maintained, and what triggers their disassembly? We will (a) Test the roles of two newly discovered apically-localized transmembrane proteins in apical domain organization~ (b) Test if downregulation of one of these proteins is involved in EMT-like withdrawal~ and (c) Identify additional genes required for tube maintenance. Our experiments take advantage of the system's very simple anatomy and powerful imaging and genetic approaches possible in C. elegans to address central questions about unicellular tubes that are also relevant to the biology of all tubes.